Question

I’m trying to create my own custom sound effects Audio Unit based on the input from the mic. This application allows simultaneous input/output from the microphone to speaker. I can apply effects and work using the simulator, but when I try to test on the iPhone I can’t hear anything. I paste my code if anyone can help me:

  - (id) init{
    self = [super init];

    OSStatus status;

    // Describe audio component
    AudioComponentDescription desc;
    desc.componentType = kAudioUnitType_Output;
    desc.componentSubType = kAudioUnitSubType_RemoteIO;
    desc.componentFlags = 0;
    desc.componentFlagsMask = 0;
    desc.componentManufacturer = kAudioUnitManufacturer_Apple;

    // Get component
    AudioComponent inputComponent = AudioComponentFindNext(NULL, &desc);

    // Get audio units
    status = AudioComponentInstanceNew(inputComponent, &audioUnit);
    checkStatus(status);

    // Enable IO for recording
    UInt32 flag = 1;
    status = AudioUnitSetProperty(audioUnit,
                                  kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Input,
                                  kInputBus,
                                  &flag,
                                  sizeof(flag));
    checkStatus(status);

    // Enable IO for playback
    status = AudioUnitSetProperty(audioUnit,
                                  kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Output,
                                  kOutputBus,
                                  &flag,
                                  sizeof(flag));
    checkStatus(status);

    // Describe format
    AudioStreamBasicDescription audioFormat;
    audioFormat.mSampleRate         = 44100.00;
    audioFormat.mFormatID           = kAudioFormatLinearPCM;
    audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    audioFormat.mFramesPerPacket    = 1;
    audioFormat.mChannelsPerFrame   = 1;
    audioFormat.mBitsPerChannel     = 16;
    audioFormat.mBytesPerPacket     = 2;
    audioFormat.mBytesPerFrame      = 2;


    // Apply format
    status = AudioUnitSetProperty(audioUnit,
                                  kAudioUnitProperty_StreamFormat,
                                  kAudioUnitScope_Output,
                                  kInputBus,
                                  &audioFormat,
                                  sizeof(audioFormat));
    checkStatus(status);
    status = AudioUnitSetProperty(audioUnit,
                                  kAudioUnitProperty_StreamFormat,
                                  kAudioUnitScope_Input,
                                  kOutputBus,
                                  &audioFormat,
                                  sizeof(audioFormat));
    checkStatus(status);


    // Set input callback
    AURenderCallbackStruct callbackStruct;
    callbackStruct.inputProc = recordingCallback;
    callbackStruct.inputProcRefCon = self;
    status = AudioUnitSetProperty(audioUnit,
                                  kAudioOutputUnitProperty_SetInputCallback,
                                  kAudioUnitScope_Global,
                                  kInputBus,
                                  &callbackStruct,
                                  sizeof(callbackStruct));
    checkStatus(status);

    // Set output callback
    callbackStruct.inputProc = playbackCallback;
    callbackStruct.inputProcRefCon = self;
    status = AudioUnitSetProperty(audioUnit,
                                  kAudioUnitProperty_SetRenderCallback,
                                  kAudioUnitScope_Global,
                                  kOutputBus,
                                  &callbackStruct,
                                  sizeof(callbackStruct));
    checkStatus(status);


    // Allocate our own buffers (1 channel, 16 bits per sample, thus 16 bits per frame, thus 2 bytes per frame).
    // Practice learns the buffers used contain 512 frames, if this changes it will be fixed in processAudio.
    tempBuffer.mNumberChannels = 1;
    tempBuffer.mDataByteSize = 512 * 2;
    tempBuffer.mData = malloc( 512 * 2 );

    // Initialise
    status = AudioUnitInitialize(audioUnit);
    checkStatus(status);

    return self;
}

This callback is called when new audio data from the microphone is available. But never enter here when I test on the iPhone:

static OSStatus recordingCallback(void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList *ioData) {
    AudioBuffer buffer;

    buffer.mNumberChannels = 1;
    buffer.mDataByteSize = inNumberFrames * 2;
    buffer.mData = malloc( inNumberFrames * 2 );

    // Put buffer in a AudioBufferList
    AudioBufferList bufferList;
    bufferList.mNumberBuffers = 1;
    bufferList.mBuffers[0] = buffer;

    // Then:
    // Obtain recorded samples

    OSStatus status;

    status = AudioUnitRender([iosAudio audioUnit],
                             ioActionFlags,
                             inTimeStamp,
                             inBusNumber,
                             inNumberFrames,
                             &bufferList);
    checkStatus(status);

    // Now, we have the samples we just read sitting in buffers in bufferList
    // Process the new data
    [iosAudio processAudio:&bufferList];

    // release the malloc'ed data in the buffer we created earlier
    free(bufferList.mBuffers[0].mData);

    return noErr;
}

Answer 1

I solved my problem. I simply needed to initialize the AudioSession before playing/recording. I did so with the following code:

OSStatus status;

AudioSessionInitialize(NULL, NULL, NULL, self);
UInt32 sessionCategory = kAudioSessionCategory_PlayAndRecord;
status = AudioSessionSetProperty (kAudioSessionProperty_AudioCategory,
                               sizeof (sessionCategory),
                               &sessionCategory);

if (status != kAudioSessionNoError)
{
    if (status == kAudioServicesUnsupportedPropertyError) {
        NSLog(@"AudioSessionInitialize failed: unsupportedPropertyError");
    }else if (status == kAudioServicesBadPropertySizeError) {
        NSLog(@"AudioSessionInitialize failed: badPropertySizeError");
    }else if (status == kAudioServicesBadSpecifierSizeError) {
        NSLog(@"AudioSessionInitialize failed: badSpecifierSizeError");
    }else if (status == kAudioServicesSystemSoundUnspecifiedError) {
        NSLog(@"AudioSessionInitialize failed: systemSoundUnspecifiedError");
    }else if (status == kAudioServicesSystemSoundClientTimedOutError) {
        NSLog(@"AudioSessionInitialize failed: systemSoundClientTimedOutError");
    }else {
        NSLog(@"AudioSessionInitialize failed! %ld", status);
    }
}


AudioSessionSetActive(TRUE);

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